Signal for trunk-lines of telephone systems.



No. 649,959. Patented May 22, 1900.

C. E. SCRIBNER.

SIGNAL FOB TRUNK LINES 0F TELEPHONE SYSTEMS.

(Application filed June 17, 3898.)

(No Model.)

Witnesses: Inventor;

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ATENT CnAntEs E. SCRIBNER, or CmCAeo, ILLINOIS, ASSIGNOR To 'riniWESTERN ELECTRIC COMPANY, on SAME PLACE.

SIGNAL FOR TRUNK-LINES OF TELEPHONE SYSTEMS.

$PECIIIGA'IION forming part of Letters Patent No. 649,959, dated May 22,1900. Application filed June 17, 1898. Serial No. 683,742. (No model.)

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Be it known that I, GHARLEs E. SCRIBNER, a citizen of the United States,residing at Chicago, in the county of Cook'and State of Illinois, haveinvented a certain new and useful Improvement in Signals for Trunk-Linesof Telephone Systems, (Case No. e68 of which the following is a full,clear, concise, and exact description. 7

This invention applies to trunk-lines between central offices oftelephone-exchange systems.

It consists in a system of visible signals, with means for operatingthem to enable the attendant at one terminal station of the trunkline tomake, supervise, and remove connections between the trunk-line andsubscribers lines with a high degree of efficiency and with a slightliability to error.

In the employment of trunk-lines between offices of extensive exchangesthe greatest efficiency is attainable in using any trunkline to extendconnections in only one direction-that is, from the office within whichthe calls originate to that wherein the connections are to becon1plctedbusiness in the reverse direction being accommodated bytrunk-lines assigned solely for such connections.

The terminal of the trunk-line with which connection is made from theline of a subscriber calling is frequently referred to as theoriginating or A terminal, the attendant who makes the connection beingtermed the A operator. The other extremity of the trunk-line, which isemployed in completing the connection to the line of the partycalled, isdesignated the incoming 01"B terminal and the attendant the B operator.The functions of the A operator consist in answering the call of thecalling subscriber, making connection with the trunk-line, instructingthe B operator to make the connection between a trunk-line and the linecalled for, supervising the connection while it exists, and removing theconnection at the A terminal in response to the subscribers call fordisconnection. The functions of the B operator consist in assigning tothe A operator the trunk-line which is to be used, testing the linecalled for, making connection with the line, sending the call-signal tothe station thereof, and removing the connection of the trunk-line withthe line of the called subscriber in response to a signal from the Aoperator. The agencies employed by the A operator consist of theapparatus by means of which she makes ordinary connections; but theapparatus at the B terminal of the trunk-line is of a special naturedesigned to give the B operator the special information which sherequires. This apparatus is so constructed, however, as to permit theoperation of the apparatus at the A terminal in its usual manner inorder that the A operator may not be confused in her Work by amultiplicity of signals with different meanings.

The mechanism and signals at the B terminal of the trunk-line shouldperform the following functions: The mechanism should provide a circuitby means of which the operator may test the line to determine whether itbe free for use. A signal should be provided to indicate the response ofthe called party to the Call-signal; but this signal should not be againdisplayed during the connection. A signal should be displayed when the Aoperator breaks the connection with the trunkline; but this signalshould be so arranged that the called subscriber can attract theattention of the B operator in the event of accidental disconnection atthe A switchboard. The present invention is addressed to these variousrequirements and is adapted for use in connection with means forautomatically controlling the different signals referring to thetelephone-lines automatically in the use of the terminal telephones. Itsprincipal features consist in the combination, with a subscribers linewith means for determining the flow of current in the line in the use ofthe telephone and a trunk-line for temporary association with thesubscribers line, of a testing-telephone at the B terminal, anelectromagnetic switch for connecting the telephone with a test-contactof the plug, and a circuit for operating the switch to disconnect thetelephone when connection is made with the line, a signal referring tothe line of the called party, means for controlling it in response tocurrents in the called line determined in the use of the telephone, anda device for preventing the display of the signal after the response ofthe called party, a clearing-out signal, a relay associated with thetrunk line, means for producing current through the relay, and circuitconnections forming two paths for current therein, one controlled by aswitch at the A terminal of the trunk-line and the other controlled atthe station of the called line.

A further feature of the invention consists in an improved constructionand mode of arrangement of the relay for controlling the clearing-outsignal, whereby the static balance of the trunk-line is maintained.

The invention is shown diagrammatically in the attached drawing. Thisdrawing represents two telephone-substations with lines enteringswitchboards in different central offices, a trunk-line between theoflices, and signaling mechanism in accordance with the presentinvention associated with the trunk line.

For the purpose of controlling signals the circuits through thecall-bells at the stations at and a are interrupted, as respectscontinuous currents, by condensers interposed in the conductors. Thusthe line-circuits are placed in condition to permit the flow of a steadycurrent through them only when the telephones are taken from theirswitches for use. In other respects the equipment at the substations isof usual and well-known character. From station a line conductors l and2 lead to spring-jacks b in a switchboard at the central office 0.Associated with the same line are a relay (1, with a secondaryline-signal d controlled by it, and a cut-off relay e. Both conductorsof the line-circuit are prolonged from the spring jack through theswitch-contacts of the cut-off relay, after which they are unitedthrough a battery f, the magnet-windin g of relay (1 being included inthe line conductor 2. The magnet of cutoff relay 6 is located in agrounded conductor 3, which leads to normally-insulated contactrings 5of the spring-jacks b. The switchboard is furnished with the usual pairsof plugs h and 72., together with the conductors 4 and 5, uniting them,constituting the plugcircuit, and the usual calling key 71, andlisteningkey h The conductive continuity of the plug-circuit isinterrupted by the interposition therein of a repeating-coil 72 twoserially-connected windings ot' the repeating-coil being located in eachconductor of the plug-circuit, with a bridge uniting the points ofjunction of the pairs of windings. In this bridge of the plug-circuit abattery its is interposed. In the portion of the conductor 5 at eachside of the bridge a relay is placed, these relays being designated hand 7&7, respectively, whose function is to control signal-lamps k h",respectively, referring to the different lines with which plugs h and hmay become connected. The lamps arein the circuit of conductors 6 and 7,respectively, which terminate in sleeve-contacts of plugs h and h,designed to register with the contact-rings b of the spring-jacks intowhich they may be inserted, their other terminals being led to the freepole of a grounded battery h Relays h and h7 control the current throughthe lamps 7L8 and h, respectively, through the agency of shunts 8 and 9,including the switch-contacts of the relays.

A trunk-line 1O 11 extends from the office c to the office 2, whereinthe line from station a terminates. This trunk-line is designed to beused in making connections from calling lines in the oflice c to linescalled for in the office i. The conductors of the line terminate incontact-pieces of a spring-jack j before the A operator at the office 0,similar in arrangement and function to the springjacks of a subscribersline. The contactring I) of this jack forms the terminal of a conductorwhich includes a coil of resistance equal to that of the magnet-windingof relay e. At its other terminal in oflice i the conduc tors of thetrunk-line are completed during the use of the line to the line-contactsof a plug is. Signal-lamps Z and m are associated with this terminalplug, the former designed to serve as a line-signal referring to theline of a called party and the latter as a clearingout signal. Thecircuits of these signals, together with other circuits associated withthe trunk-line, are controlled by three relays n, 0, 19, respectively.The relay n has a single pair of switch-contacts a M, which becomeclosed when the relay is excited, but its magnet is provided with twowindings n and n. The relay 0 is of somewhat similar construction,having also a single pair of switchcontacts 0' and 0 and twomagnet-windings o and 0 The relay 1) is provided with two switch-springsp and 19 which are actuated by the armature. The former of these has anormal resting-contact p and an alternate con tact 29 against which itis thrust when the relay is excited, while the latter spring has only analternate contact 19 The switchcontacts 19 19 control the continuity ofone conductor of the trunk-line extending to the tip is of plug 70, thetip of the plug being connected with the switch-spring p and the lineconductor 10 being led to the anvil p. The normal resting-anvil p of theswitch-spring forms the terminal of a conductor 13 in the circuit of thetelephone (1 of the B operator. The magnet of relayp and the signal-lampl are included serially in a conductor 1A, which leads from a battery 0'to the local contactpiece of plug 7c. The switch-spring 10 1s connectedwith the free pole of the same grounded .battery, and its contact-anvil19 forms the terminal of a grounded conductor 15, which includes thesignal-lamp m. The

conductor leading from --the battery to the switch-contact 29* containsa resistance-coil. This coil may have a resistance approxi mately equalto that of the lamp m.

The conductor 11 of the trunk-1ine is normally continuous to thesleeve-contact k of plug 70; but it traverses one winding 01 of relay a.The other winding a of this relay, together with the switch-contacts 'nniwhich the magnet controls, are interposed in a conductor 16, which isdesigned to form a shunt about the lamp Z.

The windings o o of the relay oare located in a bridge 18 of thetrunk-circuit-lO 11, together with a condenser s. This bridge isconnected with the free pole of battery 1'. The switch-contacts o o ofthis relay control a wire 17, which when it is closed forms a shuntabout the signal-lamp m. The purpose of providing two windings on therelay 0 in a completed bridge of the circuit with a condenser interposedbetween thewindings is to maintain the static balance of the trunk linewhile retaining an operative connection of the relay with the line. Thewindings of the relay should be of many turns to attain high impedancein the magnet.

The circuit of the line conductors to the plug traverses theswitch-contacts of the usual calling-key z, for bringing a generator ofcalling-current into circuit with the plug.

Communication may be established between the telephones of the A and Boperators by means of an order-wireli), which permanently includes thereceiving-telephone of the B operator at office 2, but which may bebrought into connection with the telephone of the A operator through theagency of a key under the control of the latter operator.

In the operation of this system the mere removal of the telephone fromits switch at station a for use brings about the display of theline-signal cl, and thus indicates a call to the operator at otlice c.In response to this call the operator will insert plug 7t into aspring-jack b of the calling line, at the same time bringing hertelephone into connection with the plug circuit, and thus through oralcommunication will learn the subscribers ordersay for connection withstation a entering the office i. The insertion of a plug into thespring-jack of a calling line completes a local circuit 6 3 of battery hwhereby the cut-off relay 0 is excited and breaks the normal groundconnections of the calling line. At the same time the circuit completedfrom battery 71 through the conductors of the plug-circuit effects theexcitement of relay h, which closes the shunt 8 about the lamp it.Having learned the order of the calling subscriber, the A operatorbrings her transmitting-telephone into circuit with the ordenwire 19 andaddressing the B operator at the office 0 instructs this operator tomake connection with the line to station a. The B operator, observingthat the trunk-line 1O 11 is free for use, informs theA operator thatthis trunleline will be used in making connection, whereupon the Aoperator inserts plug h into the spring-jack j. This act of the Aoperator completes a local circuit 7 12 of battery it by which the lampit is lighted. The battery 7r finds as yet no circuit through theconductor 5 ot' the plug- -remains dark.

circuit and the conductor ll of the trunkline, so that the shunt aboutlamp It remains broken and the lamp continues to be lighted. lVhile theA operator is completing her portion of the work of making connectionbetween the lines, the B operator, taking the plug It, tests the line tostation a by applying the tip of plug 7- to the test-ring b of aspring-jack of the line called for. If this line he in use in virtue ofa connection already existing with the line, a battery it or 7 will beconnected with the test-rings of these spring-jacks and a current willflow to the tip of the plug and thence through the conductor 13 toearth, producing a characteristic test-sound in the telephone of the Boperator. If the line be not in use, no such current will result fromthe application of the plug to the springjack. Finding the line free foruse, the B operator inserts the plug into the spring-jack of the linecalled for and transmits a calling current to the station thereof bymeans of the key 25. Putting the plug 7tinto the spring-jack Z) closesthe local circuit of battery 7* through conductors 143.116. 3, wherebythe relay 1) and the lamp Z are excited. The magnetization of therelay-magnet brings the switch-springs p p against their respectiveanvilsp p whereby the conductor 10 of the trunk-line is made continu ousto the tip-contact of the plug 7c, and thus to conductor 1 of thelinecircuit, While the connection of the tip of the plug with theoperators telephone q is broken and a local circuit is closed by way ofwire 15, which provides current for exciting the signal-lamp m. Thecurrent in signal-lamp Z lights this lamp, whose display indicates tothe B operator that the line-circuit at the station called is open. Theinsertion of plug 7L into the spring-jack 7 at othce 0 provides a pathfor current from battery 7' through winding 0 01? relay 0, through theconductor 10 of the trunkline, and through a portion of conductor at ofthe plug-circuit to earth, whereby the relay 0 is excited and is causedto complete the shunt 17 about the lamp m. Hence When this clearing-outlamp m becomes connected with an excitingbattery 0' it is shuntedthrough the iustrumentality of relay 0 and When the called subscriber,responding to the signal, takes his telephone for use, the line-circuitbecomes closed at the substation, current flows from battery 7L5 througha portion of conductor 5 ot' the plug-circuit, conductor 11 of thetrunk-line, and conductor 2 of the line-circuit, returning by way ofline conductor 1, trunk-line conductor l0, and conductor at of theplug-circuit. The currentin this circuit excites both relays 7L7 and uat the offices 0 and 2', respectively. The magnetization of the formerrelay brings about the completion of shunt 9 about supervisorysignal-lamp 7L9, whereby the A operator is informed of the response ofthe called subscriber. The magnetization of relay or effects the closureof shunt 10 of super- 4 c ients;

visory lamp Z, darkening this lamp, and at the same time provides aclosed local circuit including the winding n of the relay n, whereby therelay is prevented from subsequent control by current through thetrunk-line. Hence the signal-lamp Z will remain dark while theconnection exists. The purpose of the lamp Z is to permit the B operatorto send a second or subsequent call-signal to the called station if thefirst signal should receive no response or in the event of obtain ing noresponse to inform theA operator that the called party cannot be made toanswer.

' When this condition has been reached, the

. remains at the office 0.

stations at and a are in telephonic communication. The supervisory lampsh and h in the switchboard at oflice c are dark, and thus indicate thatthe telephones at the terminal substations are in use. The lamps Z and mbefore the B operator indicate to her, respectively, that the partycalled for has responded and that connection with the trunk-line Thereplacement of the telephone on its switch at either station a or aafiects only the signals h and h, the return of either telephone to itsswitch being indicated by the lighting of the corresponding signal. Whenboth signals have become illuminated, the A operator may assume that theconversation has been finished and may withdraw plugs h and hfrom thespringjacks into which they are inserted. The Withdrawal of plug h fromthe spring'jack j breaks the circuit of battery r through the conductorsl0 and 4, and since the circuit from battery 1* through thetelephone-line is already broken the relay 0 is deprived of current andbreaks the shunt 17 about the clearing-out lamp m. This lamp thenreceives current from battery 1-, which lights it, and its displayinstructs the B operator to remove the terminal plug of the trunk-linefrom the spring-jack into which it is inserted. Its removal breaks thecircuit through relays n and p, whereby all the apparatus and signalsare permitted to return to their normal conditions.

The invention is defined in the following claims:

1. The combination with two telephonelines, each provided with means atits station for controlling a current in the line automatically in theuse of the telephone, said lines terminating in different offices, of atrunkline between the olfices uniting the said subscribers lines, asource of current at one of the offices in a bridge of the unitedcircuits, an electromagnet at the other ofiice in the path of currenttherefrom to the line entering the said office, and a supervisory signalcontrolled by the magnet, as described.

'2. In combination with telephone -lines, each having at its station aswitch for controlling a current in the line in the use of thetelephone, said lines entering different offices,

of a trunk-line uniting the telephone-lines, a bridge of the unitedcircuits and a source of current therein at the originating office, anelectromagnet in the path of current therefrom to the called line ateach of said offices, one of said magnets being located at each office,and a supervisory signal controlled by each of said electromagnets, asdescribed.

3. The combination with telephone-lines having telephone-switches attheir substa tions controlling currents in the line in the use of thetelephones, said lines entering different offices, of a trunk-lineuniting the said lines, a bridge of the united circuits at theoriginating office and a source of current therein, an electromagnet inthe path of cur rent therefrom to the calling line, two electromagnetsin the paths of current therefrom to the called line, saidlast-mentioned magnets being located at the ditferent'offices, andsupervisory signals controlled by each of the electl'oma'g-nets, asdescribed.

at. The combination with telephone-lines and means at the stationsthereof for controlling currents in the lines in the use of thetelephones, said lines entering different offices, of atrunk-lineuniting the lines, abridge of the completed circuit and a source ofcurrent therein, an electromagnet in the path/of current to the callingline, two electromagnets, located at the different offices, in the pathof current to the called line, a local circuit of the electromagnet atthe B terminal of the trunk-line including a winding of theelectromagnet there, together with switchcontacts closed by the saidmagnet when excited, means for closing the local circuit at anotherpoint in the use of the trunk-line, and supervisory signals controlledby the magnets at the difierent offices; whereby the supervisory signalsat the A office indicate at all times the position of the telephones atthe substations, while the supervisory signal at the B office iscontrolled from the called substation only when the telephone is broughtinto use, as described.

5. The combination with a trunk-line for uniting telephone-linesentering different offices, of an electromagnet having two windingsconnected in a bridge of the trunk-line,

a condenser interposed between the said windings, a source of currentconnected to one of the windings, and a clearing-out signal controlledby the electromagnet, whereby the balance of the line as respectsinductive disturbances is maintained, as described.

In witness whereof I hereunto subscribe my name this 2d day of April, A.D. 1898.

CHARLES E. SCRI BNER.

WVitnesses:

ELLA EDLER, MYRTA F. GREEN.

